From 088a0075c5eb44979181ec294a6681be148c2c4c Mon Sep 17 00:00:00 2001
From: wm4 <wm4@nowhere>
Date: Fri, 5 Aug 2016 16:01:26 +0200
Subject: w32_common: don't wait for GUI thread when polling for events

VOCTRL_CHECK_EVENTS is called on every frame. This is by design, and is
supposed to check the event queue of the windowing API.

With the decoupled GUI thread in w32_common.c this doesn't make too much
sense, and the purpose of VOCTRL_CHECK_EVENTS is really reduced to
checking event flags. Even worse, waiting on the GUI thread can
interfere with playback, since win32 sometimes blocks the event loop
(e.g. clicking the window title bar).

Change the code such that we really only query the event flags. Use
atomics to avoid having to add a new mutex. (We assume we always have
real atomics available. The build system doesn't check this properly,
and it could fall back to dummy atomics, which are not atomic.)

Should help with #3393. Doesn't help if the core happens to send a
synchronous request, most commonly via VOCTRL_SET_CURSOR_VISIBILITY or
VOCTRL_UPDATE_PLAYBACK_STATE.
---
 video/out/w32_common.c | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/video/out/w32_common.c b/video/out/w32_common.c
index e78e94157a..4934a433b2 100644
--- a/video/out/w32_common.c
+++ b/video/out/w32_common.c
@@ -95,7 +95,7 @@ struct vo_w32_state {
 
     bool disable_screensaver;
     bool cursor_visible;
-    int event_flags;
+    atomic_uint event_flags;
 
     BOOL tracking;
     TRACKMOUSEEVENT trackEvent;
@@ -569,7 +569,7 @@ static bool handle_char(struct vo_w32_state *w32, wchar_t wc)
 
 static void signal_events(struct vo_w32_state *w32, int events)
 {
-    w32->event_flags |= events;
+    atomic_fetch_or(&w32->event_flags, events);
     vo_wakeup(w32->vo);
 }
 
@@ -1498,8 +1498,7 @@ static void do_control(void *ptr)
     void *arg = p[3];
     int *ret = p[4];
     *ret = gui_thread_control(w32, request, arg);
-    *events |= w32->event_flags;
-    w32->event_flags = 0;
+    *events |= atomic_fetch_and(&w32->event_flags, 0);
     // Safe access, since caller (owner of vo) is blocked.
     if (*events & VO_EVENT_RESIZE) {
         w32->vo->dwidth = w32->dw;
@@ -1510,10 +1509,15 @@ static void do_control(void *ptr)
 int vo_w32_control(struct vo *vo, int *events, int request, void *arg)
 {
     struct vo_w32_state *w32 = vo->w32;
-    int r;
-    void *p[] = {w32, events, &request, arg, &r};
-    mp_dispatch_run(w32->dispatch, do_control, p);
-    return r;
+    if (request == VOCTRL_CHECK_EVENTS) {
+        *events |= atomic_fetch_and(&w32->event_flags, 0);
+        return VO_TRUE;
+    } else {
+        int r;
+        void *p[] = {w32, events, &request, arg, &r};
+        mp_dispatch_run(w32->dispatch, do_control, p);
+        return r;
+    }
 }
 
 static void do_terminate(void *ptr)
-- 
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